Modeling the effect of film-pore coupled transport on composite forward osmosis membrane performance

The methods used to quantify membrane structural contributions to transport resistance in osmotic processes contain inherent assumptions and inaccuracies. Consequently, incomplete information is available on the actual effects of the support layer and overall composite membrane characteristics, on performance. In this work, the effects of support properties such as pore radius, porosity and thickness on membrane transport are studied using a 2D numerical model that accounts for coupled transport of water and solute within both the selective thin-film and the support pores. The results indicate that reducing support thickness by half enhanced performance to a greater extent (~40–50% increase in net driving force recovered) than did either doubling porosity (22–34% increase in net driving force recovered) or increasing pore radius by two orders of magnitude (15–28% increase in net driving force recovered). Further, the effect of the support pore radius, not included in the commonly employed structural parameter equation (which includes porosity, tortuosity and thickness), was found to impact performance. It was seen that the individual geometrical features comprising the structural parameter affect performance to varying degrees and thus future membrane design could benefit from tuning these parameters accordingly, so as to achieve optimal performance.